Answers : (1)

if both frames are at rest w.r.t each other then the acceleration seen by each frame is same as other

so option a is correct.

if there is constant relative velocity is between the frames then also the both see the acceleration of any particle to be same

so option c is also correct

if the relative acceleration is zero then also they observe any particle to be moving with same acceleration

if the relative acceleration of frames w.r.t particle is 'a' but in opposite directions then the magnitude of acceleration of the particle w.r.t both frames is 'a' but the relative acceleration between the frames is 2a